Abstract
Natural photosynthesis can be divided between the chlorophyll-containing plants, algae and cyanobacteria that make up the oxygenic phototrophs and a diversity of bacteriochlorophyll-containing bacteria that make up the anoxygenic phototrophs. Photosynthetic light harvesting and reaction centre proteins from both kingdoms have been exploited for solar energy conversion, solar fuel synthesis and sensing technologies, but the energy harvesting abilities of these devices are limited by each protein’s individual palette of pigments. In this work we demonstrate a range of genetically-encoded, self-assembling photosystems in which recombinant plant light harvesting complexes are covalently locked with reaction centres from a purple photosynthetic bacterium, producing macromolecular chimeras that display mechanisms of polychromatic solar energy harvesting and conversion. Our findings illustrate the power of a synthetic biology approach in which bottom-up construction of photosystems using naturally diverse but mechanistically complementary components can be achieved in a predictable fashion through the encoding of adaptable, plug-and-play covalent interfaces.
Highlights
Natural photosynthesis can be divided between the chlorophyll-containing plants, algae and cyanobacteria that make up the oxygenic phototrophs and a diversity of bacteriochlorophyllcontaining bacteria that make up the anoxygenic phototrophs
Protein concentrations used for the fluorescence measurements were too low for this drop in LHCI emission to be attributable to reabsorption by the added reaction centres (RCs), and an equivalent drop was not seen for LHCII and WT RCs at similar concentrations (Fig. 2a)
As it is known that the emission quantum yield of LHCI in vitro is much more sensitive to its environment than is the case for LHCII36, the observed drop in LHCI emission on adding WT RCs is attributed to a change in its intrinsic quantum yield rather than being a signature of energy transfer
Summary
Natural photosynthesis can be divided between the chlorophyll-containing plants, algae and cyanobacteria that make up the oxygenic phototrophs and a diversity of bacteriochlorophyllcontaining bacteria that make up the anoxygenic phototrophs. Our everyday experience of photosynthesis is dominated by the blue/red-absorbing pigment chlorophyll, a magnesium tetrapyrrole that acts as both a harvester of solar energy and a carrier of electrons and holes Variants of this versatile molecule, principally chlorophyll a and chlorophyll b, are found in the plants, algae and cyanobacteria that make up the oxygenic phototrophs. A striking observation is the complementary nature of the absorbance spectra of chlorophyll and bacteriochlorophyll photosystems (Fig. 1a) This is enabled by the somewhat different electronic structures of their principal pigments (Supplementary Fig. 1a) and facilitates the occupancy of complementary ecological niches by oxygenic and anoxygenic phototrophs. Anoxygenic phototrophs harvest parts of the solar spectrum which oxygenic phototrophs do not absorb well, and vice versa
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